1. Field of the Invention
The present invention relates to a structure for preventing cavitation erosion mainly applied to gear type oil pumps for diesel engines. The oil pump is constructed such that pump gears engaging each other are accommodated in a pump case in a state in which the gap between a side face of the gear and a side wall face of a gear room of the pump case and/or the gap between the other side face of the pump gear and the side end face of the pump cover are very small so that oil leakage through the gaps is a minimum and oil is discharged from the pump by the rotation of the pump gears.
2. Description of the Related Art
Gear pumps such as, for example, disclosed in Japanese Laid-Open Patent Application No. 2002-266613, in which a gear pump has gears driven by a pump drive gear connected to a crankshaft of an engine to supply lube oil to the engine, are widely used for diesel engines.
In such a gear pump for feeding oil, gears engaging each other are accommodated in a pump case in a state in which the gaps between both the side faces of the gears and the side wall face of a gear room of a pump case and the pump gear side end face of the pump cover are very small so that oil leakage through the gaps is a minimum, in order to prevent reduction in volumetric efficiency.
In the gear pump as disclosed in JP2002-266613A, oil introduced in tooth grooves in the suction room of the oil pump is discharged to the tooth grooves in the discharge room of the oil pump as the gears engaging each other are rotated. When oil is excluded from the tooth groves in the meshing part, a part of the oil is enclosed in the meshing part and compressed therein to high pressure, and leaks through the side gaps at the meshing part to the suction room where oil pressure is low.
The side gaps are made very small to a minimum in order to attain high volumetric efficiency of the pump. So, the high pressure oil enclosed in the meshing part flows through the very small gaps at very high speed toward the suction room where oil pressure is low, and cavitation tend to occur at the very small side gaps near the meshing part and cavitation erosion tends to occur there.